net: tracepoint of net_dev_xmit sees freed skb and causes panic
Because there is a possibility that skb is kfree_skb()ed and zero cleared
after ndo_start_xmit, we should not see the contents of skb like skb->len and
skb->dev->name after ndo_start_xmit. But trace_net_dev_xmit does that
and causes panic by NULL pointer dereference.
This patch fixes trace_net_dev_xmit not to see the contents of skb directly.
If you want to reproduce this panic,
1. Get tracepoint of net_dev_xmit on
2. Create 2 guests on KVM
2. Make 2 guests use virtio_net
4. Execute netperf from one to another for a long time as a network burden
5. host will panic(It takes about 30 minutes)
Signed-off-by: Koki Sanagi <sanagi.koki@jp.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/trace/events/net.h b/include/trace/events/net.h
index 5f247f5..f99645d 100644
--- a/include/trace/events/net.h
+++ b/include/trace/events/net.h
@@ -12,22 +12,24 @@
TRACE_EVENT(net_dev_xmit,
TP_PROTO(struct sk_buff *skb,
- int rc),
+ int rc,
+ struct net_device *dev,
+ unsigned int skb_len),
- TP_ARGS(skb, rc),
+ TP_ARGS(skb, rc, dev, skb_len),
TP_STRUCT__entry(
__field( void *, skbaddr )
__field( unsigned int, len )
__field( int, rc )
- __string( name, skb->dev->name )
+ __string( name, dev->name )
),
TP_fast_assign(
__entry->skbaddr = skb;
- __entry->len = skb->len;
+ __entry->len = skb_len;
__entry->rc = rc;
- __assign_str(name, skb->dev->name);
+ __assign_str(name, dev->name);
),
TP_printk("dev=%s skbaddr=%p len=%u rc=%d",
diff --git a/net/core/dev.c b/net/core/dev.c
index c7e305d..9393078 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2096,6 +2096,7 @@
{
const struct net_device_ops *ops = dev->netdev_ops;
int rc = NETDEV_TX_OK;
+ unsigned int skb_len;
if (likely(!skb->next)) {
u32 features;
@@ -2146,8 +2147,9 @@
}
}
+ skb_len = skb->len;
rc = ops->ndo_start_xmit(skb, dev);
- trace_net_dev_xmit(skb, rc);
+ trace_net_dev_xmit(skb, rc, dev, skb_len);
if (rc == NETDEV_TX_OK)
txq_trans_update(txq);
return rc;
@@ -2167,8 +2169,9 @@
if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
skb_dst_drop(nskb);
+ skb_len = nskb->len;
rc = ops->ndo_start_xmit(nskb, dev);
- trace_net_dev_xmit(nskb, rc);
+ trace_net_dev_xmit(nskb, rc, dev, skb_len);
if (unlikely(rc != NETDEV_TX_OK)) {
if (rc & ~NETDEV_TX_MASK)
goto out_kfree_gso_skb;